Current events, e.g., the discovery of toxins in toys, environmental air and water concerns, and resulting regulations dictate an urgent need for an analyzer for toxic element determination. Advanced x-ray fluorescence (XRF) analyzers can play a valuable role in the quantification of such toxins and many other substances of interest in a variety of samples, e.g., toxins in consumer products, and various harmful elements in petroleum products.
As one prominent example, manufacturers, suppliers, distributors, retailers, and regulatory entities need a long-term solution for toxic-element analysis for a wide variety of consumer goods. Many new regulations require manufacturers to detect many elements such as lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd), chromium (Cr), bromine (Br), selenium (Se), antimony (Sb), barium (Ba), and chlorine (Cl). In the EU regulations, the maximum concentration in a homogenous material is 1,000 ppm for hexavalent chromium (Cr6+), Hg, Pb, polybrominated biphenyl (PBB), and polybrominated diphenyl ethers (PBDE), and 100 ppm for Cd. The new U.S. regulation (CPSIA) for children's products is much more restrictive. For example, the maximum allowable lead level in toys and children's jewelry is less than or equal to 100 ppm in any accessible part of a product.
Current measurement methods are either accurate enough but not usable on the factory floor, or they may be convenient for use on the factory floor but not close to being sufficiently sensitive or repeatable. As a result, there is a need for a truly fit-for-purpose analyzer for this application. There is a strong market need for a rapid, reliable, convenient, nondestructive, high-sensitivity, quantitative, cost-effective analyzer to carry out critical and conclusive measurements with a single instrument in a manufacturing facility either at-line or on-line, or any place in a distribution chain. Contaminated products can be eliminated at the most advantageous place in the process, substantially mitigating or even eliminating accidental production waste and errors. There is also a strong need for a similar capability at several stages in the distribution and by regulators to verify the compliance of materials and products.
Existing low-cost methods of toxin detection are generally ineffective, e.g., swab tests. Higher-cost methods that provide the requisite accuracy are expensive and time consuming. These methods may involve manually scraping samples, digesting them in acids at elevated temperature and pressure, introducing them into a combustion chamber, and analyzing the combustion product. One widely used method is inductively coupled plasma optical emission spectroscopy (ICP-OES)—a method which is expensive, destructive, and slow. Alternatively, conventional handheld x-ray fluorescence (XRF) guns are rapid and nondestructive, but are only reliable for higher than regulated concentrations, and are averaged across large sample areas, and cannot separately evaluate paint layers.
As discussed further below, the present invention provides a measurement solution with fast, accurate results for toxins in manufactured products, enabled by sophisticated x-ray sample excitation and monochromating optic techniques. Such proprietary optics typically provide 10-1,000× improvements in the ability to focus x-rays; and optic-enabled analyzers are especially suited for these targeted markets—moving measurements from the lab into the factory, field, and clinic.
In x-ray analysis systems, high x-ray beam intensity and small beam spot sizes are important to reduce sample exposure times, increase spatial resolution, and consequently, improve the signal-to-background ratio and overall quality of x-ray analysis measurements. In the past, expensive and powerful x-ray sources in the laboratory, such as rotating anode x-ray tubes or synchrotrons, were the only options available to produce high-intensity x-ray beams. Recently, the development of x-ray optic devices enables collection of the diverging radiation from an x-ray source by focusing the x-rays. A combination of x-ray focusing optics and small, low-power x-ray sources can produce x-ray beams with intensities comparable to those achieved with larger, high-power, and more expensive devices. As a result, systems based on a combination of small, inexpensive x-ray sources, excitation optics, and collection optics are greatly expanding the availability and capabilities of x-ray analysis equipment in, for example, small laboratories and in the field, factory, or clinic, etc.
Monochromatization of x-ray beams in the excitation and/or detection paths is also useful to excite and/or detect very precise portions of the x-ray energy spectrum corresponding to various elements of interest (lead, etc.). X-ray monochromatization technology is based on diffraction of x-rays on optical crystals, for example, germanium (Ge) or silicon (Si) crystals. Curved crystals can provide deflection of diverging radiation from an x-ray source onto a target, as well as providing monochromatization of photons reaching the target. Two common types of curved crystals are known as singly-curved crystals and doubly-curved crystals (DCCs). Using what is known in the art as Rowland circle geometry, singly-curved crystals provide focusing in two dimensions, leaving x-ray radiation unfocused in the third or orthogonal plane. Doubly-curved crystals provide focusing of x-rays from the source to a point target in all three dimensions. This three-dimensional focusing is referred to in the art as “point-to-point” focusing.
Commonly-assigned U.S. Pat. Nos. 6,285,506 and 7,035,374, incorporated by reference herein in their entirety, disclose various configurations of curved x-ray optics for x-ray focusing and monochromatization. In general, these patents disclose a flexible layer of crystalline material (e.g., Si) formed into curved optic elements. The monochromating function and the transmission efficiency of the optic are determined by the crystal structure of the optic.
The ability to focus x-ray radiation to smaller spots with higher intensities, using focusing and monochromating x-ray optics, has enabled reductions in the size and cost of x-ray tubes, and x-ray systems have therefore been proliferating beyond the laboratory to in-situ, field uses. Commonly-assigned U.S. Pat. Nos. 6,934,359 and 7,072,439, incorporated by reference herein in their entirety, disclose monochromatic wavelength dispersive x-ray fluorescence (MWD XRF) techniques and systems, using doubly curved crystal optics in the excitation and/or detection paths. The x-ray optic-enabled systems described in these patents have enjoyed widespread success beyond the laboratory, for example, measuring sulfur in petroleum fuels in a variety of refinery, terminal, and pipeline environments.
In such systems, precise optic alignment along an axis defined by a source and sample spot may be required, as illustrated in above-incorporated U.S. Pat. No. 7,035,374, which proposes an arrangement of curved, monochromating optics around a central axis operating according to Bragg diffraction conditions. FIG. 1a is a representative isometric view of this x-ray optic arrangement 150 having a curved optic 152, an x-ray source location 154, and an x-ray target location 156. X-ray source location 154 and x-ray target location 156 define a source-to-target transmission axis 162. Optic 152 may include a plurality of individual optic crystals 164, all of which may be curved and arranged symmetrically about axis 162. The plurality of crystals 164 may be arranged from a small fraction of a rotation to a full rotation around the source-to-target transmission axis 162.
FIG. 1b is a cross-sectional view taken along section lines 1b-1b of FIG. 1a, wherein the surface of optic 152, x-ray source location 154, and x-ray target location 156 define one or more Rowland (or focal) circles 160 and 161 of radius R for optic 152. Those skilled in the art will recognize that the number and orientation of the Rowland circles associated with crystal optic 152, or individual crystals 164, will vary with the position of the surface of optic crystal 152, for example, the variation of the toroidal position on optic crystal 152.
The internal atomic diffraction planes of optic crystal 152 also may not be parallel to its surface. For example, as shown in FIG. 1b, the atomic diffraction planes of crystal 152 make an angle γl with the surface upon which x-rays are directed, at the point of tangency 158 of the surface and its corresponding optic circle 160 or 161. θB is the Bragg angle for crystal optic 152 which determines its diffractive effect. Each individual optic crystal can in one example be fabricated according to the method disclosed in above-incorporated U.S. Pat. No. 6,285,506, entitled “Curved Optical Device and Method of Fabrication.”
All individual crystals 164 should be aligned to the source-to-target axis 162, for proper Bragg conditions. Improvement in optic alignment, especially for such multiple-crystal optics, therefore remains an important area of interest. Various optic/source combinations have already been proposed to handle thermal stability, beam stability, and alignment issues, such as those disclosed in commonly assigned U.S. Pat. Nos. 7,110,506; 7,209,545; and 7,257,193. Each of these patents is also incorporated herein by reference in its entirety.
The above-described XRF technology and systems have been useful in single-element analyzers for measuring generally homogeneous sample structure (e.g., sulfur in petroleum products). However, the measurement of toxins in manufactured products presents additional levels of challenges. First, an instrument should have the capability to measure more than one element simultaneously or near-simultaneously, from a relatively confined list, for example, the 10 toxic elements, discussed above. Moreover, manufactured products are likely to be heterogeneous in nature, requiring small spot resolution, as well as the ability to detect toxins in one of a number of heterogeneous layers (e.g., the level of lead in a paint layer and separately in a substrate layer beneath the paint).
Improved x-ray analysis method and systems are required, therefore, to address the problems associated with measuring multiple toxins in potentially heterogeneous samples, to enable in-the-factory and/or in-the-field measurement of toxins.